ID 21

Micro-explosion characterization thanks to optical diagnostics during the heating of W/O droplets

 

Abstract:

“Micro-explosion” is a thermal phenomenon that can happen when an emulsion droplet is heated, at one condition: The two non-miscible fluids (for our case water and n-tetradecane) must have different boiling points. In this case, the dispersed phase (water) reaches its saturation temperature faster than oil, resulting in a sudden phase change that leads to a volumetric expansion and thus, the atomization of the continuous phase (n-tetradecane). However, micro-explosion is not a systematic process and other phenomena like “puffing” (partial micro-explosion) can take place. It appears that micro-explosion occurrence is strongly related to physical properties of the fluids, but mostly to the size distribution of the water dispersed droplets. For this reason, two optical diagnostic technics have been developed. The first one consists on the observation of an emulsion droplet at 500°C thanks to a CCD at high frequency (2000-3000 Hz). The second one consists on adding a fluorescent dye, Fluorescein, that is soluble only in water. The emulsion droplet is then heated in the same conditions, and excited by a continuous laser plane sheet. The emitted light is filtered before being recorded by the CCD camera. Thanks to these two technics, we are able to record the evolution of the size distribution of water droplets and identify the optimal ones for a higher micro-explosion occurrence, study the motion of the dispersed droplets and other phenomenon like dynamics of the coalescence of dispersed droplets.